IV. BCMath 任意精度数学函数库

简介

PHP 为任意精度数学计算提供了二进制计算器 (Binary Calculator)，他支持任意大小和精度的数字，以字符串形式描述。

需求

自 PHP 4.0.4 以来，libbcmath 都绑定在 PHP 内部。这个扩展不需要其它外部库的支持。

安装

These functions are only available if PHP was configured with --enable-bcmath. In PHP 3, these functions are only available if PHP was not configured with --disable-bcmath.

PHP 的 Windows 版本已经内置该扩展模块的支持。您无需加载任何附加的扩展库即可使用这些函数。

运行时配置

这些函数的行为受到全局配置文件 php.ini 的影响。

表格 1. BC math configuration options

Name	Default	Changeable
bcmath.scale	0	PHP_INI_ALL

For further details and definition of the PHP_INI_* constants see ini_set().

以下是该配置选项的简要解释。

bcmath.scale integer: Number of decimal digits for all bcmath functions. See also bcscale().

资源类型

该扩展模块未定义任何资源类型。

预定义常量

该扩展模块未定义任何常量。

目录
bcadd -- Add two arbitrary precision numbers
bccomp -- Compare two arbitrary precision numbers
bcdiv -- Divide two arbitrary precision numbers
bcmod -- Get modulus of an arbitrary precision number
bcmul -- Multiply two arbitrary precision number
bcpow -- Raise an arbitrary precision number to another
bcpowmod -- Raise an arbitrary precision number to another, reduced by a specified modulus
bcscale -- Set default scale parameter for all bc math functions
bcsqrt -- Get the square root of an arbitrary precision number
bcsub -- Subtract one arbitrary precision number from another

add a note User Contributed Notes
BCMath 任意精度数学函数库

benjcarson at digitaljunkies ca
08-Jul-2002 07:17

Note that bcmath doesn't seem to handle numbers in exponential notation
(i.e. "1e4"), although PHP considers such a value a
number.

example:

$exp1 = "1E5";
$exp2 =
"2E4";
$ans1 = bcadd($exp1, $exp2, 3);
$ans2 = $exp1 +
exp2;
echo("bcadd: $exp1 + $exp2 = $ans1");
echo("php:
$exp1 + $exp2 = $ans2");

// Output:
bcadd: 1E5 + 2E4 =
0.000
php: 1E5 + 2E4 = 120000

Just a gotcha if you're using
passing PHP numbers into bcmath functions...

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